Anchorage, Alaska (CNN) -- Two decades ago, Roy Dalthorp helped clean up the rocky shores of Prince William Sound after the tanker Exxon Valdez ran aground, producing what was then the largest oil spill in U.S. history.

Today, with that record surpassed by the 11-week-old disaster in the Gulf of Mexico, Dalthorp struggles to breathe. He coughs, and his failing eyes sometimes tear up uncontrollably.

Dalthorp told CNN that he was "slowly poisoned" during the Alaska cleanup effort -- and he says some of those now working to clean up the BP spill off Louisiana and neighboring states are risking the same fate.

BP says it is working with federal health and environmental regulators to make sure cleanup workers are protected from the hazards of the Gulf spill. But observers like Rikki Ott, an environmental activist who studied the Exxon Valdez spill, said cleanup workers in the Gulf are showing "the exact identical symptoms down here that we had 21 years ago."

Dalthorp says his troubles started when the then-out-of-work oil worker joined the Exxon Valdez cleanup effort. For six weeks, he lived and worked aboard a ship that ran boilers to heat sea water. The 120- to 140-degree water was used to blast crude off the shoreline, and it left plumes of oily-smelling steam in the surrounding air.

"I had no choices, because I was behind on my house payments, and no health insurance," he said.

Soon he began to cough. Teams from the Environmental Protection Agency were monitoring the cleanup, but "nobody ever checked with us," Dalthorp said.

Tanker owner Exxon paid to study the effects of the spill on nearly every creature that came into contact with the 11 million gallons that were dumped into Prince William Sound -- except people.

"Clams and mussels, to fish and otters, to ducks and eagles, and even deer and bears," said Anchorage lawyer Dennis Mestas, who represented another worker who was involved in the cleanup. "But they never studied what this oil was doing to the workers -- to the human beings in Prince William Sound."

Mestas warns history may be repeating itself thousands of miles away in the Gulf of Mexico, with evidence of workers getting sick, and their medical records being controlled by BP.

Dalthorp never filed a workers compensation claim or had a doctor determine the cause of his illness. But Mestas said the man he represented -- Gary Stubblefield, who he said "still struggles for each breath" as a result of the cleanup -- sued Exxon over his illness. The oil company settled for a reported $2 million, without admitting any blame, after Mestas went to an Exxon office in Houston, Texas, and viewed medical records of cleanup workers.

Exxon had asked the court to keep those records under seal to protect the workers' privacy. But Mestas said the company was forced to let him view summaries of the health records of 11,000 cleanup workers, and found that 6,722 of them had gotten sick.

In a statement issued to CNN, Exxon -- now ExxonMobil -- said it could not confirm that number. The workers hired for the cleanup "tended to be transient, temporary workers, making any medical follow-up incredibly difficult," it said. And it noted that out of roughly 50,000 workers hired for the effort, "there were no adverse judgments rendered against the company."

"After 20 years, there is no evidence suggesting that either cleanup workers or the residents of the communities affected by the Valdez spill have had any adverse health effects as a result of the spill or its cleanup," the company said.

The issue has drawn the attention of the House Energy and Commerce Committee, which has been holding hearings on the Gulf disaster. On July 1, the committee asked ExxonMobil to turn over all records related to the health of workers who took part in the Alaskan cleanup. The company says it is reviewing the request.

At the time, the government and the company called those illnesses the "Exxon crud," a flu or cold that Exxon was not required to report to federal health officials. The National Institute for Occupational Safety and Health agreed, but Mestas said the agency "never looked at any medical records," which were controlled by Exxon.

"The only epidemiology was that there were a few head colds that they could identify, and NIOSH didn't have any of the records," he said.

ExxonMobil told CNN that the institute had "full access to Exxon's records" during its study.

Since the Gulf spill erupted in April, CNN has been receiving reports of fishermen hired to take part in the cleanup effort developing upper respiratory illnesses, nausea and vomiting.

Louisiana's state health department reported 128 cleanup workers believed to have been sickened by exposure to oil by the end of June, with symptoms like dizziness, nausea and breathing issues. On a video provided to CNN by a state health official, one hospitalized fisherman says that "a lot of the other guys" had the same complaints.

In a statement to CNN issued Wednesday, citing state figures, BP said 21 people had "short hospitalizations."

"Most workers reported having had symptoms that cleared up quickly resulting from exposures attributed to a variety of chemicals," the company said. But it said that so far, air testing conducted by the EPA and the Occupational Safety and Health Administration have not found "a single reading above OSHA regulations to date." And the company says there is no need to issue respirators to the cleanup workers based on those results.

BP says a database of injury and illness data is shared daily with state and federal health officials. It has 25 first-aid stations in the field and a clinic in Venice, Louisiana, that is run by federal officials.

But Ott, a marine biologist who studied the effects of the 1989 Exxon Valdez spill, says the symptoms being reported in the Gulf states are the same ones that hit workers in Alaska. And just like then, people with their backs against the wall financially are flocking to the take jobs with the cleanup.

"I'm feeling like BP is forcing them into this situation where BP holds all the cards, and BP is letting these workers get sick," Ott said.